In the past it has been customary to manufacture garage door sections in standard lengths of 8, 10, 12, 14 and 16 feet and of a variety of widths. In some steel construction it is, for example, customary to find an opening of two inches in excess of a standard eight-foot opening, requiring special sections to be made up. It is also desirable to provide a lightweight door consistent with proper insulating properties; for example, in high openings required for commercial trucks, the weight of the door is considerable. There have been some proposals to provide lightweight doors, as in the Stroup U.S. Pat. No. 2,880,796, but this construction requires special and expensive metallic edge extrusions. Similarly, another lightweight door is shown in Kloote et al. U.S. Pat. No. 2,907,383, but here there is no proper provision for the mounting of the necessary door hardware that will survive rough service, plugs in the weak plastic-filled portion being utilized. The present invention overcomes these prior art weaknesses and provides a door section that can be made in a long length and cut for each installation.